1. Field of the Invention
The invention relates to a process for the addition of silanes or siloxanes which have SiH groups but are free of substituents which, after splitting off from the silicon atom, act as proton acceptors, to compounds with olefinic double bonds in the presence of catalysts of the platinum group.
2. Description of the Prior Art
The use of platinum catalysts for the addition of silanes or siloxanes with SiH groups to compounds with one or more olefinic double bonds is known and described, for example, in the book "Chemie und Technologie der Silicone" (Chemistry and Technology of the Silicones), Chemie Publishing House, 1960, page 43, and in the patent literature, for example, in German Offenlegungsschrift No. 26 46 726. In this connection, H.sub.2 PtCl.sub.6.6H.sub.2 O is mentioned as the preferred catalyst.
This addition reaction, however, proceeds without an appreciable formation of by-products only if the compounds which have the olefinic double bonds are free of groups which can react with the SiH group in competition with the addition reaction. This includes particularly the carbon-linked hydroxyl group. The competing reactions can be represented as follows:
______________________________________ 1. Addition reaction: ##STR1## 2. Competing Reaction: ##STR2## ______________________________________
In practice, it frequently happens that hydrogen silanes or hydrogen siloxanes must be added to compounds with olefinic unsaturations, which also have hydroxyl groups or other reactive groups. An example of such a reaction is the addition of a hydrogen siloxane to an alcohol or polyether of the following general formula. ##STR3## in which
n=0 to 10,
x=0 to 100,
y=0 to 100, and when
x and y=0, n.gtoreq.1.
Such conversion products of polyether alcohols with hydrogen siloxanes play an important role as foam stabilizers in the production of polyurethane foams as well as surfactants in other areas of application, for example, in the cosmetics, paint and textile industries.
There is thus a need for a catalyst which, on the one hand, has a high activity with respect to the addition of the SiH group to olefinic double bonds and, on the other, minimizes the side reactions. Besides the aforementioned competing reaction in the form of the reaction of the SiH group with the COH group, it is desired to also avoid disproportionation reactions within the silane or siloxane compounds. Such disproportionation reactions are understood to include a redistribution of the SiH groups usually present in the mixture of silanes or siloxanes.
Further side reactions or secondary reactions are the conversion of the allyl groups used into propenyl groups or the possible crosslinking of the addition compounds having terminal OH groups via an acetal formation with the propenyl ether groups. Both reactions are promoted by acidic catalysts, such as, for example, H.sub.2 PtCl.sub.6.6H.sub.2 O and lead, on the one hand, to an inadequate conversion of the SiH groups and, on the other, to an increase in viscosity of the end product.